This multidisciplinary Program Project Grant (PPG) is focused on elucidation of fundamental mechanisms that control differentiation and contractile function of vascular smooth muscle cells (SMC) during normal development and maturation, as well as how these control processes are altered in response to vascular injury or diseases such as atherosclerosis, post-angioplasty re-stenosis, and hypertension that are characterized by SMC dysfunction. The Projects are mutually interdependent, highly synergistic, and converge on investigation of a common theme of understanding SMC differentiation, growth, and contractile function. The PPG includes a unique team of internationally recognized investigators with complementary interests and expertise. Project 1 A. Somlyo) is focused on determining the role of the smooth muscle myosin light chain kinase (MLCK) in egulation of development of SMC (with Projects 2 and 3), regulation of cross bridge cycling, and assembly of myosin filaments. Studies also include identification of the kinase(s) responsible for force generation in MLCK knockout mice generated during the current funding period, and collaborative studies examining the role of cytoskeletal remodeling in control of SMC gene expression (Project 2) and differentiation of coronary SMC (Project 3). Project 2 (G. Owens) is focused on determining cellular and molecular mechanisms that control the growth and differentiation of SMC during vascular development, and how these control processes are altered during phenotypic switching of SMC in association with vascular injury or experimental atherosclerosis. Studies include determining the role of myocardin/myocardin-like factors in mediating changes in SMC marker gene expression in response to contractile agonists or PDGF BB that activate or repress SMC gene expression respectively. Studies involve extensive use of unique transgenic and conditional knockout mice generated during the current funding period. Project 3 is new to this PPG and is headed by Dr. Majesky. The goal of this project is to determine the function of vertebrate hedgehog (hh) proteins in coronary SMC development and repair. The project includes extensive joint studies with Project 2 to determine the role ofmyocardin and other SRF co-activators in hh-induced differentiation of coronary SMC, as well as collaborations with both Projects 1 and 2 investigating the role of MLCK and cytoskeletal alterations in differentiation of coronary SMC. A Microscopy Core (Core A) will promote collaborative interactions.